The present invention relates to liquid discharge apparatus for discharging a liquid at a high velocity. The invention is particularly useful when implemented in a portable inoculation gun for anti-virus inoculation of plants, and is therefore described below with respect to such an implementation, but it will be appreciated that the invention could advantageously be implemented in many other types of liquid-discharge device.
It has been known for many years, but not widely appreciated, that plants can be protected from a severe, deliberating virus by prior infection with a mild strain of a closely related virus. This is known as cross-protection. As described in our prior International Application PCT/IL00/00039 (U.S. Pat. No. 6,644,341), the contents of which are incorporated herein by reference, the mild viruses previously introduced for cross-protection had to be inoculated by hand-rubbing mechanical friction. This confined the number of plants that could be infected and restricted the use of the method to instances where labor costs are negligible or the value of each plant is high. Moreover, the inoculation efficiency (i.e. the percentage of plants successfully infected) by the hand-friction method is usually not high enough for commercially relevant protection. Application PCT/IL/00/00039 described a multi-barrel plant inoculation gun which facilitated, for the first time, robust inoculation of up to 250,000 plantlets in a working day, compounded by very high efficiencies. However, the method of that application is restricted to use in nurseries where trays bearing plantlets are transported on a conveyer belt and are subject to jet-propulsion from the machine as described therein. Such a method can only be used with respect to young plantlets before transfer to the field, and not with respect to plants directly sown in the field or, for example, fruit trees.